To enable submitting batches of scsi commands by the backing stores,
NOT_LAST bit is added to the command state.
This integrates the batching feature seamlessly both for the LLDs and the
backing stores:
- the backing stores not supporting batched mode can safely disregard NOT_LAST
bit and submit all commands separately (as previously);
- the LLDs can also ignore the bit and not set it at all, as the default
value NOT_LAST=0 means that each command is "last" (i.e. separately submitted,
in this context), so that even the backing stores which do support batching
will make no attempt to batch it.
- when both LLD and BS support batching, the LLDs which accumulate scsi cmds
may submit them marking all but the last one with NOT_LAST=1. The BS is
hinted to queue the commands marked with NOT_LAST=1 until a command marked
NOT_LAST=0 is submitted, then all the commands previously queued can
be submitted, if approppriate. The NOT_LAST=0 bit only instructs the BS that
the currently available batch is complete, so that more commands may
not arrive for quite a long time, but the BS may decide to actually
separate or combine these "batches" according to its own algorithms.
Signed-off-by: Alexander Nezhinsky <alexandern@xxxxxxxxxxxx>
---
usr/scsi_cmnd.h | 2 ++
1 files changed, 2 insertions(+), 0 deletions(-)
diff --git a/usr/scsi_cmnd.h b/usr/scsi_cmnd.h
index c764c4e..6e3c6e2 100644
--- a/usr/scsi_cmnd.h
+++ b/usr/scsi_cmnd.h
@@ -100,6 +100,7 @@ enum {
TGT_CMD_QUEUED,
TGT_CMD_PROCESSED,
TGT_CMD_ASYNC,
+ TGT_CMD_NOT_LAST,
};
#define CMD_FNS(bit, name) \
@@ -119,3 +120,4 @@ static inline int cmd_##name(const struct scsi_cmd *c) \
CMD_FNS(QUEUED, queued)
CMD_FNS(PROCESSED, processed)
CMD_FNS(ASYNC, async)
+CMD_FNS(NOT_LAST, not_last)
--
1.7.1
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